PREFACE INASMUCH as Sir W. H. Flower and Mr. Lydekker could not profess to treat the Mammalia exhaustively within the limits of nearly 800 pages, in their Introduction to the Study of Mammals, it is obvious that the present volume, which appears ten years later and is of rather less size, can contain but a selec- tion of the enormous mass of facts at the disposal of the student of this group. Thus the chief question for myself was what to select and what to leave aside, It will be observed that I have reduced the pages of this book to conformity with those of other volumes of the series by treating some groups more briefly than others. It has appeared to me to be desirable to treat fully such groups as the Edentata and the Marsupialia, and permissible to be more brief in dealing with such huge Orders as those of the Rodentia and Chiroptera. Lengthy disquisitions upon Fuch familiar and comparatively uninteresting animals as the Lion and Leopard have been curtailed, and the space thus saved has been devoted to shorter and more numerous accounts of other creatures. As there are nearly six hundred genera of living Mammals known to science, omission as well as compression became an absolute necessity* I have given, I hope, adequate treatment from the standpoint of a necessarily limited treatise to the majority of the more important genera of Mammals both living and extinct; but the length of this part of the book had to be increased by the dis- coveries, which give me at once an advantage and a diaadvantage as compared with the two authors whose names I have quoted, of a considerable number of important new types in the la&t ten years.